The invention relates generally to power-driven conveyors conveying articles and more particularly to conveyor systems using accelerometers to measure the acceleration of a conveyor conveying articles.
One purpose of a conveyor, such as a conveyor belt, is to transport products or persons smoothly, either through a larger device or from one point to another in a manufacturing, logistic, or transport operation. Smooth, linear motion of the conveyor is important in many applications, such as, for example, transporting passengers, manufacturing extrusions, and conveying unstable products subject to tipping upright. But many variables cause the motion of conveyor belts not to be smooth. These variables include, but are not limited to, fluctuations in the belt's drive train, resonances in the conveyor belt, resonances in other coupled systems, and fluctuating loading caused by people walking over the surface of the belt. The fluctuations and resonances affect the conveyor belt's forward motion by causing speed changes, i.e., accelerations, which can jostle passengers, topple cans or bottles, or degrade a continuous manufacturing process. This problem is particularly evident in long conveyor systems because the accumulated elasticity of the long belt makes it difficult to control the belt's dynamic motion. In people movers, for example, as a passenger walks or moves about on top of the belt, his shifting foot weight sets up a periodic load that acts as a forcing function. The spring constant of the long belt allows the belt to expand and compress to a degree that is noticeable and objectionable to the passenger on the belt. The dynamic motion of the belt becomes problematic. While shifting foot weight is the cause of the forcing function in this example, long belts are more elastic and more subject to resonance. Thus, there is a need for smoothly moving conveyors.
All mechanical devices generate periodic accelerations due to the motion of components such as linkages, gears, chains, and pistons. Even uniformly rotating components, such as shafts, flywheels, and disks, generate periodic accelerations due to imbalance and run-out. Components such as roller bearings in larger devices also generate characteristic periodic accelerations. These accelerations or vibrations in one or more dimensions can be measured by accelerometers. Analyzing accelerometer data using methods such as Fourier analysis can isolate these various sources. As mechanical components wear, their frequency spectra and magnitudes change over time. This information can be used to predict failure trends and support planned maintenance. Traditionally, accelerometers are permanently affixed to devices or temporarily affixed using magnetic mounts, clips, or similar methods. Multiple accelerometers located throughout a mechanical device provide desirable local information of the device, but are prohibitive because of cost and physical constraints, such as mounting and routing of wires. Thus, there is a need for economically measuring and analyzing the wear characteristics of mechanical systems to predict failures.